The present invention relates generally to flexible tubes for endoscopes and, more particularly, to a new and improved flexible tube for endoscopes and a method for manufacturing the same characterized by the arrangement and manner of formation of a coating of the flexible tube.
Generally, conventional flexible tubes for endoscopes are formed of a basic tubular core structure consisting of a metallic tubular spiral, sometimes referred to as FLEX, whose outer surface is covered by a meshwork tube, the outer surface of the tubular core structure itself being covered in one of two ways. In a first construction, a previously molded synthetic resin tube has covered the basic tubular core structure while in a second typical construction, a thermoplastic elastic body is directly molded around the tubular core structure so as to cover the same.
In the flexible tube of the first type described above, the basic tubular core structure is not adhered to the premolded synthetic resin tube and, consequently, wrinkles are often formed in the outer surface of the flexible tube as the latter is guided around a curved path during the introduction of the flexible tube into the body cavity. Another problem is that the flexible tube is not sufficiently rigid in compression so as to resist the compressive forces on the tube caused during the introduction thereof into the body cavity. Moreover, the well known flexible tubes of this type have also lacked good torsional rigidity, i.e., have poor rotation following characteristics, so that twists are often caused to be formed in the flexible tube by ordinary rotary manipulation thereof and such twists once formed frequently cause the flexible tube to become caught between inner walls or folds of the body cavity. Thus, introduction of such conventional flexible tubes is often painful to the patient and it is not always possible achieve a smooth introduction in any event. Furthermore, twists formed in the flexible tube can prevent the physician operating the endoscope from observing a desired region or object at a certain location through the forward end of the flexible tube.
In the conventional flexible tube construction of the latter type described above, some of the thermoplastic elastic material often protrudes through gaps present in the basic tubular core structure so as to extend into the inner surface of the flexible tube thereby causing an unevenness therein, such protrusion of the thermoplastic elastic material occurring in an uneven manner. As a result, it has frequently not been possible to obtain a uniform coating wall thickness relative to the central axis of the flexible tube. This fact has made it difficult to obtain a homogeneous flexible tube and adversely affects the flexibility of the tube which, of course, must be uniform when the flexible tube is bent during its introduction. In order to alleviate this problem, an arrangement is disclosed in Japanese patent publication No. 1980-17577 in which the basic tubular core structure is first coated with latex through immersion, drying, and solidification steps and the like, whereupon the latex covered core structure is then coated with thermoplastic material which is, in turn, molded thereon. Although this arrangement avoids the protrusion of the thermoplastic material into the basic tubular core structure, it has often resulted in complicated manufacturing processes while requiring large-sized molding machines. Accordingly, this arrangement has not been widely adopted.